1. Field of the Invention
The present invention relates to a method of braking a dehydrating vessel in a washing machine which uses a switched reluctance (SR) motor as a rotary power source of the dehydrating vessel, capable of minimizing a noise generated when stopping the SR motor.
2. Description of the Related Art
Generally, a washing machine is one of the electric appliances which cleans laundries by generating a current of water after putting water and detergent into a washing vessel together with the laundries and dehydrates wet laundries which finishes cleaning using the centrifugal separation by rotating the wet laundries which are put in a dehydrating vessel.
The above-described washing machine uses a motor as the rotary power source for rotating the dehydrating vessel. Recently, a washing machine which integrates the washing vessel and the dehydrating vessel and in which the overall washing process is controlled by a microcomputer has been developed. Accordingly, breaking from the level which only supplies the rotary power source for rotating the dehydrating vessel, the motor in which forward rotation/reverse rotation and braking operations are controlled by the microcomputer is preferably used so that the washing performance can be enhanced by creating the current of water effectively.
There are various kinds of motors which satisfy such a requirement. Out of them, as a device for economizing the manufacturing cost, a switched reluctance (SR) motor which satisfies the above-described requirement and is relatively inexpensive has recently been adopted.
FIG. 1 is a view of an embodiment illustrating the inner structure of the conventional SR motor. As shown in the drawing, in the SR motor 10, an armature coil 10b binds a core of a stator 10a which is arranged around a rotor 10c located at the rotary shaft. Accordingly, in the case of electrifying the armature coil 10b, a torque is generated by the magnetic attractive force which functions between the rotor 10c and the core of the stator 10a which is magnetized. By electrifying the armature coils on each A, B and C phase, successively, the rotor 10c is rotated. In the drawing, the SR motor 10 having 3 phases which has 6 stators and 4 rotors is disclosed. This SR motor can be manufactured to have multielectrode and polyphase.
FIG. 2 is a view illustrating an operation control circuit for controlling the operation of the SR motor having three phases. The operation control circuit includes inverter unit 20 having pairs of transistors Q1 and Q2; Q3 and Q4; and Q5 and Q6 which apply current to each armature coil La, Lb and Lc of the SR motor 10 from the power source according to the electrifying signal applied to base terminals; current feedback diodes D1 through D6. Pairs of transistors Q1 through Q6 are electrified when the electrifying signal is applied to the their base terminals and electrify the armature coils La, Lb and Lc by applying the current which has the same phase as the electrifying signal and vary the excitation state of the cores of the A, B and C phases, there by controlling the operation of the SR motor 10.
Here, it is important to detect the location of the rotor, as the rotating direction is decided according to the positions of the stator 10a and rotor 10c when the core of the stator 10a is magnetized by electrifying the armature coils La, Lb and Lc of each phase and the rotor 10c can be rotated and stopped. Generally, inside of the SR motor 10, as shown in FIG. 3, a sensor plate 11 having a plurality of through holes 11a is connected to the rotor 10c, and an optical sensor (not illustrated) composed of a light transmitting element and a light receiving element is located facing the through hole 11a. As the light transmitted from the light transmitting element is incident upon the light receiving element via the through holes 11a of the sensor plate 11, a predetermined detection signal is generated, and thereby the position and the speed of the rotor 10c can be detected thereon.
As the electrifying signal to be applied for the operation control circuit is decided according to the position of the detected rotor 10c, it is possible to decide the rotating direction of the SR motor 10 or rotate or stop the rotor 10c.
FIG. 4A is a view illustrating the shape of an inductance according to the relative positions of a stator and a rotor in the SR motor; FIG. 4B is a view illustrating a wave form of an electrifying signal applied to an armature coil for rotating the SR motor; and FIG. 4C is a view illustrating a wave form of an electrifying signal applied to an armature coil for stopping the SR motor.
As shown in FIG. 4A, as the rotor 10c approaches to the core of the A-phase, the inductance increases. When the rotor 10c coincides with the core of the A-phase, the inductances reaches at its maximum. As the rotor 10c goes apart from the core of the A-phase, the inductance decreases.
As described above, around when the rotor 10c and the core of A-phase coincides each other, it is possible to rotate or stop the SR motor 10 according to the point of time when the armature coil of A-phase is electrified. As shown in FIG. 4B, when the rotor 10c approaches to the core of A-phase of the stator 10a, in the case that the armature coil of A-phase is electrified and the core of A-phase is magnetized, a torque is generated at the rotor 10c in the rotating direction due to the magnetic attractive force functioning from the core of the magnetized A-phase.
On the contrary, as shown in FIG. 4C, when the rotor 10c goes apart from the core of A-phase of the stator 10a, in the case that the armature coil of A-phase is electrified and the core of the A-phase is magnetized, a torque is generated at the rotor 10c in the reverse rotating direction due to the magnetic attractive force functioning from the core of the magnetized A-phase. Moreover, assuming that a duty ratio of the current applied to the armature coil is varied, the strength of the torque generated at the rotor can be controlled.
As described above, the microcomputer of the washing machine controls the operation of the SR motor 10 by controlling the phase of the electrifying signal to be applied for the operation control circuit or varying the duty ratio, thereby allowing forward/reverse rotation or stopping the rotor.
The SR motor is relatively inexpensive comparing with another motors. However, it causes a noise when stopping the motor.
Especially, in the case that the door of the washing machine is opened during the dehydrating vessel rotation, it is necessary to stop the dehydrating vessel within a limited short time (it is indicated as `safety time limit`) for user's safety. The safety time limit is prescribed as about 10 seconds. In this case, the microcomputer can stop the dehydrating vessel within the safety time limit by allowing the core of the stator 10a to have large magnetic attractive force after applying the current having a large duty ratio to the armature coil. At this time, as the dehydrating vessel which is rotated at a high speed is stopped within in a short time, the noise is generated from the SR motor.
Moreover, in the case that the dehydrating vessel is rotated at a low speed, the microcomputer stops the dehydrating vessel by applying the current having the same duty ratio as when the dehydrating vessel is rotated at a high speed to the armature coil. At this time, the time for stopping the dehydrating vessel rotating at a low speed becomes shorter than the dehydrating vessel which is rotated at a high speed. However, the degree of the noise is the same as when stopping the dehydrating vessel which is rotated at a high speed.